The present invention relates to an improvement in the processes for the continuous spinning of viscose rayon.
Processes for the continuous spinning of viscose rayon are known, in which viscose, extruded from suitable spinnerets into a coagulating bath, undergoes coagulation and drawing in the same bath or in successive baths, and passes thereafter over a support and advancing apparatus which causes it to travel in a substantially helical path, viz. a path constituted by a series of successive coils which are not exactly helical but close to it; the yarn undergoing a series of treatments while it travels in said path, until it reaches the desired final characteristics. A type of apparatus adapted for causing the coagulated and drawn yarn to travel in a substantially helical path, and to which reference will be made hereinafter, is constituted of a main roller, having a relatively large diameter, and a series of secondary rollers having much smaller diameters, the axes thereof being set askew with respect to the preceding one. These latter rollers are normally called advancing rollers. The main roller is also called a treatment roller, because the chemical and thermal treatments occur on it. Since in devices of this kind, one yarn corresponds to each advancing roller, viz. a plurality of yarns concurrently travel in the apparatus and all travel on the periphery of the treatment roller and each one separately on the periphery of a distinct advancing roller, reference will be made, in describing the present invention, to an apparatus having a single advancing roller, and there fore the invention will be described with reference to only one yarn: it being understood, however, that when the invention is carried into practice, a plurality of yarns will generally be treated concurrently and consequently there will be more than one advancing roller.
The main or treatment roller, and consequently the substantially helical path of the yarn, is divided into several successive zones in the direction of travel of the yarn itself, viz. in the longitudinal direction of the treatment roller, a distinct treatment stage corresponding to each of said zones. Said various zones are normally separated by suitable, e.g. mechanical means, and one very simple separation means is constituted by flanges or pairs of flanges interposed between each zone and those adjacent thereto. Reference will be made, in describing the invention, to a device of this kind, it being understood however that the invention is independent of the particular mechanical means by which it is carried out.
In the previously known continuous processes of this type, the yarn undergoes coagulation and drawing in the same bath which it is extruded, or the yarn may be coagulated and drawn in successive baths. Alternatively, the yarn may be coagulated and drawn through a guide tube immersed in the bath and through which guide tube the bath flows over the yarn.
Thereafter, the yarn begins its helical travel, and the first operation it undergoes during this travel is an acid setting, ordinarily followed by a washing. Other treatment zones follow, which generally comprise desulphuration, bleach and finishing zones separated by washing zones, and drying zones, but the invention is not dependent on the treatments which follow the setting, as will be better understood hereinafter. The aforesaid treatment is normally carried out at yarn travel speeds not higher than 90 meters per minute, generally between 50 and 80 meters per minute. Under these operating conditions, the conventional cycle is adequate and satisfactory.
However, the need of increasing the yarn advancing speed in order to increase the production and therefore to reduce the cost of the yarn has been felt for some time. Obviously, this can be achieved by increasing the dimensions of the apparatus, in such a way that the various treatments will last the same periods of time that they last in the traditional cycle. Such a solution, however, is not desirable for cost and space take-up reasons, as well as for the difficulties of operating and maintaining an apparatus, which exceedes a certain dimension.